MITROVICA, Kosovo (AP) — Serbia's president on Saturday pledged to help build a lasting peace in Kosovo days after the killing this week of a moderate Kosovo Serb politician fueled fears of instability in the Balkans.

Amid tight security, Aleksandar Vucic paid a visit to Kosovo that officials said was designed to ease concerns among Kosovo Serbs following the slaying Tuesday of one of their leading politicians, Oliver Ivanovic.

Waving Serbian flags, hundreds of people cheered Vucic as he arrived in the Serb-dominated, northern part of the former Serbian province that declared independence in 2008. Serbia has refused to recognize the statehood of the majority ethnic Albanian Kosovo and maintains strong influence in Serb-populated areas, mostly in the north.

Upon arrival, Vucic first visited an Orthodox Serbian monastery before laying a wreath at the site of the attack on Ivanovic in the divided town of Mitrovica.

"Serbia not only wants peace, but will do its best to preserve it," Vucic said in Banjska. "We will do all we can to solve decades- and centuries-old disputes, to secure a lasting peace and security for each (ethnic) Albanian and Serbian family."

Vucic called for those responsible for Ivanovic's death to be brought to justice "without mercy." Some Serbs shouted at the Serbian president during his press conference demanding more protection from Serbia.

Later Saturday, Vucic visited a Serb family in central Kosovo.

Under EU mediation, Serbia and Kosovo have opened talks on normalizing relations in order to advance in efforts to join the European Union. The talks were due to resume this week, but were suspended after Ivanovic was gunned down in Mitrovica.

Ivanovic was a rare voice of tolerance amid persistent ethnic tensions in Kosovo, nearly two decades after the 1998-99 war.